Module 1 Lecture 1: Gastrulation and Neural Induction Flashcards
examples of protostomes
nematodes (round worms), platyhelminthes (flatworms), molluscs (snails, slugs, octopus), annelids (earthworms), arthropods (crabs, spiders, insects)
examples of deuterostomes
echinoderms (starfish, sea cucumbers), chordates (tunicates [sea squirts], vertebrates)
neuronal characteristics of sponges
no neurons, some synaptic genes
neural characteristics of radiata
neurons, diffuse nerve nets
neural characteristics of bilateria
organized nerve nets, centralized nervous systems, brains
major discovery by hodgkin & huxley
discovered ionic mechanisms of action potential propogation in squid giant axon
major discovery by Carlsson, Greengard, and Kandel
molecular basis of learning and memory in sea slug
what makes a good model organism?
accessibility, convenience, experimental advantages, momentum
characteristics of Caenorhabditis elegans as a model organism
- accessible
- convenient (live on petri dishes, females are hermaphrodites, 3 day reproductive cycle)
- experimental advantages (transparent, invariant development, connectome has been created)
- momentum
characteristics of Drosophila melanogester as a model organism
- accessible
- convenient (cheap to maintain by 1000s, 10-day reproductive cycle)
- experimental advantages
- momentum (genome 60% homologous to humans; 75% known human diseases have homologs, connectome known)
characteristics of Strongylocentrotus purpuratus
- accessible
- convenient (easy to maintain and yields large numbers of synchronized embryos)
- experimental advantages (echinoderms have bilaterally symmetric larvae, transparent embryos and larval stage)
- momentum (model for cell fate decisions of early embryogenesis)
characteristics of Danio reria as a model organism
- accessible
- convenient (spawns 100s eggs every 2-3 days, reproductive cycle 90 days)
- experimental advantages (transparent embryo, external development)
- momentum (advanced tools and techniques for forward genetic screens)
characteristics of Xenopus laevis and Gallus gallus domesticus as model organisms
- accessible
- convenient (embryos readily available)
- experimental advantages (robust, externally developing embryos, can cut, graft, and inject material, large eggs provide material for protein biochemistry)
- momentum (modern molecular techniques being incorporated)
characteristics of Mus musculus as a model organism
- accessible
- convenient (produce 8 litters of 8 pups per year, 60-day reproductive cycle)
- experimental advantages (designer mice)
- momentum (reverse genetic powerhouse)
what does ectoderm become
all outer layer (skin, hair, tooth enamel), CNS, PNS
what does endoderm become
digestive system, liver, pancreas, bladder, lungs, etc
what does mesoderm become
muscle, bone, cartilage, connective tissue, fat, circulatory and lymphatic systems, etc
what does a blastula develop from
early cell divisions after fertilization
where does the blastula invaginate to create what?
blastula invaginates at the blastopore to create the archenteron (small pocket)
blastocoel
cavity inside blastula/gastrula
mesenchyme
loosely organized mesodermal cells
animal/vegetal poles significance
non-yolky/yolky; shows that before gastrulation, blastula already polarized
protostome main feature
mouth forms from the blastopore
- mouth first
deuterostome main feature
anus forms from the blastopore
- mouth second
coelom
body cavity between digestive tract and body wall
amniote animals
primates, rodents, crocodiles, dinosaurs & birds
amniote meaning
eggs have amnion membrane surrounding embryo; exchanges gases and waste
advantages of amniote evolution
allowed animals to develop on land
- no larval stage
anamniote animals
amphibians, ray-finned fish, sharks
anamniote meaning
eggs laid in water
- facilitates gas and water exchange
where does cell division occur in a blastopore
animal pole
epiboly meaning
layer of cells spreads out from the animal pole and covers the rest of the vegetal pole
when does gastrulation occur
when epiboly reaches the bottom of the vegetal pole; forms germ layer
which pole is the blastopore closer to
animal pole
where is cell division more frequent
animal pole
where does the archenteron form
in the cavity beyond the dorsal lip
first step of avian gastrulation
posterior epiblast cells change shape and thicken, forming the primitive streak
second step of avian gastrulation
cells migrate, converging at the primitive streak and causing it to elongate
third/fourth step of avian gastrulation
the primitive streak narrows and lengthens, forming the primitive groove (the chick blastopore)
- cells migrate inward through the primitive groove and Hensen’s node
fifth step of avian gastrulation
cells generated in Hensen’s node and passing into the gastrula migrate anteriorly and form head structures and notochord
- conveyor belt moving in
what does gastrulation involve
cells moving in through the primitive streak/groove to form the three germ layers
at what point does the fertilized egg have two axes
before first cleavage
what are the two first axes of the fertilized egg
animal - vegetal axis, and dorsal-ventral axis (gray crescent)
how does the ectoderm choose between different fates?
neural induction
what is the dorsal blastopore lip derived from
the gray crescent
what determines the location of the gray crescent
where the sperm enters
what happens if the gray crescent is not equally distributed between the two halves of the fertilized egg
one tadpole develops a nervous system and the other stays as a “belly piece”
what was the outcome of the Spemann-Mangold experiment
when the dorsal lip of one embryo was transplanted into a host embryo, the host organism became conjoined to the donor embryo
what is the Spemann-Mangold organizer
the dorsal lip of the blastopore
what happens when a normal fertilized egg is treated with lithium
it becomes a hyper dorsalized embryo
what happens when a normal fertilized egg is treated with UV
it becomes a ventralized embryo
- nervous system missing, similar to belly piecew
what happens when polyA mRNA from Li-treated fertilized egg is implanted in a UV-treated fertilized egg?
a normal embryo develops
- rescues nervous system development
how did scientists determine which gene induces nervous system development
- created a cDNA library
- broke into 3 pieces, pooled it, and injected into UV-treated animals => 1 subpool rescues nervous system development
- repeat process until you get the one thing that causes nervous system development
which gene induces nervous system development
Noggin
- dose dependent manner (no Noggin = no nervous system development, lots of Noggin = full development or hyperdorsalization)
what is Noggin?
a soluble protein that induces overlying ectoderm to adopt a neural fate
what does knocking down follistatin, chordin, and noggin cause
severe loss of neural structures (loss-of-function experiment)
what do dissociated pre-gastrula animal cells grow into
neurons
what do dissociated pre-gastrula animal cells cultured with BMP grow into
skin
what do intact pre-gastrula animal caps cultured with BMP inhibitors grow into
neurons
what does BMP made by the animal cap do
inhibits neural fate
what does BMP stand for
bone morphogenic proteins
what group is BMP a part of
TGF-beta super family, a large group of secreted proteins
first step of BMP cell signaling cascade
BMP binds to its receptor from the outside of the cell
second step of BMP cell signaling cascade
the binding leads to activation of the intracellular part of the receptor
third step of BMP cell signaling cascade
activated receptor phosphorylates an intracellular protein called SMAD
fourth step of BMP cell signaling cascade
Pi-SMAD binds co-SMAD and they move to the nucleus
fifth step of BMP cell signaling cascade
in the nucleus, Pi-SMAD and co-SMAD regulate gene expression
noggin, chordin, and follistatin function
prevent BMP from binding its receptor
- signaling cascade that selects epidermal fate is not switched on
default model
the default fate of ectoderm is neural; this fate is repressed by neighboring cells through BMP signaling
- the organizer de-represses neural fate by inhibiting BMP signaling
